New SSD factor and command set - please straighten me out

[WyomingKnott]

Yes, the forum will show that I am a storage expert. But there's a lot of stuff that I haven't used.

Right now, there seem to be ongoing changes in connection format (m.2 and SATA Express), and in the command set (AHCI for SATA vs. the newer NVM Express).

As far as I can see
1) m.2 and SATA Express can expose the same bandwidth, but only if the motherboard manufacturer dedicates enough lanes to the devices.
1.1) SATA Express has exactly two PCI-e lanes
1.2) mSATA can support one, two, or four PCI-e lanes.
2) A motherboard with an m.2 socket can support only the SATA command set, or the vendor can implement the NVM-e interface.
3) An SATA Express port can support only the SATA command set, or the vendor can implement the NVM-e interface
4) Fastest performance requires NVM-e and at lease four lanes

Thanks for critiquing the above statements.

 

[patrick47018]

Does this help out any? https://www.sata-io.org/sites/default/files/documents/NVMe%20and%20AHCI%20as%20SATA%20Express%20Interface%20Options%20-%20Whitepaper_.pdf

 

[WyomingKnott]

That's good background, and confirms my understanding of NVM-e. One of the links ( www.sata-io.org/technology/sataexpress.asp) indicates that the max number of PCI-e lanes for SATA Express is indeed 2.

But I missed it if it said anything about m.2.

EDIT: I knew that diagram looked familiar! It's in the m.2 article in Wikipedia; that also says that m.2 supports NVM-e.
http://en.wikipedia.org/wiki/M.2#Features

 

[patrick47018]

Here is a more in depth comparison https://www.sata-io.org/sites/default/files/documents/NVMe_and_AHCI_long.pdf

Wow 40 pages of information, it's rather interesting

 

[JohnnyLucky]

HI!

What you are seeing is a transition from traditional consumer oriented SATA solid state drives to PCIe ssd's. It would have been a fairly straightforward process if the SATA group did not get involved. The SATA group wanted the transition to include backward compatibility with SATA ssd's. The result is a little bit of confusion about the M.2 header and compatibility.

The new SATA standard also included SATA Express which is already obsolete. Currently there are no SATA Express ssd's in the works. I have not been able to find any reports, articles, or rumors indicating that will change. The only thing a user can do is plug a standard SATA ssd into a SATA Express socket. That's it. It looks like motherboard manufacturers included SATA Express headers "just in case".

PCIe ssd's for desktop pc's are fairly simple. They are single ssd's mounted on a PCB board or adapter card that is inserted into a PCIe 3.0 or PCIe 2.0 slot on a motherboard. They normally use 2 or 4 lanes to transmit or receive data. It is my understanding that PCIe 3.0 x8 ssd's are in the works but it will be a while before we see them. These new single PCIe ssd's are not to be confused with a PCIe ssd with quad controllers like those found on the OCZ Revo or Mushkin Scorpion Deluxe drives.

PCIe ssd's for mobile and portable pc's is not that simple. Like PCIe ssd's for desktops the new M.2 interface can be either PCIe 3.0 or PCIe 2.0 and use either 2 or 4 lanes to transmit and receive data. Because the SATA group did not want to get left behind, M.2 could also support SATA ssd's. I actually have a few M.2 ssd's listed in the ssd database that are SATA 3 6Gb/s instead of PCIe.

So far it is fairly simple. It is at this point that confusion makes its appearance.

SSD manufacturers have a preference for the M.2 interface. The M.2 interface is not just for portable pc's. The interface can also be used in desktop pc's. However, their support for the new interface is not consistent. The lack of consistency is due to the interface flexibility. There are too many variations and combinations. It would have been simpler if they just used PCIe 3.0 x4 with some backward compatibility added in. You can see the confusion in the specifications. The motherboard manufacturers can't agree on proper terminology. You'll see phrases like Generation 2, Generation 4, 10Gb/s, 32Gb/s, or just plain M.2 with no further information. It is messy and the "keys" just add to the confusion. Consumers who don't do some research are going to wind up purchasing ssd's that might not be compatible with their motherboards and chipsets. I bet newegg will see an increase in RMA's.

Next up is Intel support for additional PCIe lanes. Intel is very slow when it comes to upgrades. That's why we are seeing things like if you use a particular header then a different header will be disabled because there are an insufficient number of PCIe lanes to go around. Intel made some progress with their new cpu's and chipsets but they still need to speed thing up.

Finally we have NVMe which will eventually replace ACHI. This is a new feature for consumer ssd's. Microsoft Windows 7 does not support NVMe and so far I have not seen any reports about a workaround. Windows 8.1 does support NVMe which means a Windows upgrade. If memory serves Intel will also have to make a few modifications to their chipsets. This is a wait and see what happens situation.

Currently the world's fastest consumer oriented single ssd is the Samsung SP951. It is a PCIe 3.0 x 4 ssd that supports NVMe. It is in full production and distribution as an OEM ssd. They are already showing up in HP, Lenovo, and Apple computers. Samsung has lucrative contracts to supply most of the "off the shelf" pc companies. That's why Samsung controls over 30% of the consumer ssd market. That is no small feat. With a little luck a retail version will be available in about 3 months or so at select Samsung partners like Newegg and RamCity.

Currently I know of only two motherboards that fully support two M.2 PCIe x4 ssd's - The ASRock X99 Extreme11 and the Asus X99 Deluxe. The ASRock board has two M.2 PCIe 3.0 x 4 headers. ASRock had to add extra components that added hundreds of dollars to the cost of the board. The Asus board has one M.2 PCIe 3.0 x4 header on the motherboard and one adapter card that fits in a standard PCIe 3.0 slot. For individuals who do not have any practical use for X99 desktop systems or who cannot afford an new X99 desktop system, the practical solution appears to be the use of adapter cards. Both Asus and Plextor have adapter cards that are supposed to be quite good.

 

[JohnnyLucky]

Thank You!

NVMe update - After I finished my comments I went back to checking for articles and reports about new ssd's at the big Consumer Electronics Show being held in Las Vegas this week. I've been adding the newly announced ssd's to the ssd database I maintain. I came across reports that Mushkin announced their new Hyperion PCIe ssd. It is a PCIe 3.0 x 4 ssd. It works with NVMe and ACHI. Looks like the problem is solved for Windows 7 users.